Protozoan nomina dubia: to arbitrarily restrict or replace. The case of Sarcocystis spp.

The original descriptions of some parasitic protozoa lack sufficient information to recognize where they may belong among current taxa. Descriptions were often made from fresh, unpreserved specimens and no type specimen remains. Some of the original names of Sarcocystis (Apicomplexa) were given to seemingly similar structures in a host. It is now impossible to apply them reasonably, and with any degree of scientific certainty, to any one of the 2-3 taxa of Sarcocystis known from each of several hosts and known to be host-specific. As a consequence, the original names became nomina dubia, names not certainly applicable to any known taxon. What do we do with these nomina dubia? The International Code of Zoological Nomenclature (1964) does not discuss them expressly, but implies that such names remain available (Art. 17, no. 29). Heydom et al. (1975) decided to give all the new taxa of Sarcocystis new names, in part, because there was no scientific basis for assigning any of the old names, and in part, because if a decision could only be arbitrary, the outcome should be clear, rather than ambiguous. Others suggest the arbitrary use of one of the old names for one of the new taxa, giving the other taxa new names (Melville, 1980). The issue is between arbitrariness in the interest of preserving an old specific name, and the feeling that arbitrariness is scientifically objectionable. Although either method promises precision, events lead one to question whether both means are similarly capable of achieving it. The following provides a specific illustration. When it was thought that there was only one species of Sarcocystis in cattle, Sarcocystis hirsuta Moule, 1888 had priority, and the following were synonyms: Miescheria cruzi Hasselmann, 1926, S. fusiformis Railliet, 1897 of Babudieri